Bias in IPCC AR4 WG III? A Guest Post by Richard Tol, Part IV

This post is Part IV of Richard Tol's look at the IPCC AR4 WGIII. The first three posts looked at Chapter 11. Part I is here. Part II is here. Part III is here. This installment looks at Chapter 3.

Richard Tol is a research professor at ESRI in Ireland, one of the top 175 economists in the world and a contributor to the work of the Intergovernmental Panel on Climate Change (IPCC), where his work is widely cited. In this guest post, the fourth of a series, Richard takes a look at parts of the IPCC AR4 Working Group III, which has largely escaped scrutiny in recent months. In this Part IV he concludes that a peer reviewed paper,

. . . is misrepresented – despite protests in two rounds of review – and the chapter supports the conclusion of the gray literature, without alerting the reader that these is a wider range of opinion.

Please have a look at Richard's full discussion below. If you have questions or criticisms of Richard's analysis please submit them in the comments, I am sure that Richard will be happy to engage.

Unwillingness to Reflect a Diversity of Views

In parts 1, 2 and 3, I looked at Chapter 11 of the Fourth Assessment Report of Working Group III of the Intergovernmental Panel on Climate Change.

In part 4, I turn my attention to Chapter 3 “Issues related to mitigation in the long-term context”. The first and second order draft of the chapter and the review comments can be found here:

On p. 179, we read

Lutz et al. (2004), UN (2004) and Fisher et al. (2006) have produced updated projections for the world that extend to 2100. The most recent central projections for global population are 1.4–2.0 billion (13–19%) lower than the medium population scenario of 10.4 billion used in the SRES B2 scenarios.

This is just not true. Fisher et al. (the most recent of the three publications listed, and the only one that is peer-reviewed; note that I am one of the alii) have a central projection of 11.9 billion, which is 1.5 billion higher, not lower. Fisher et al. are well aware that their results deviate, and write:

We can reproduce previous results on total population numbers, but we need to force the model hard. Fertility is the variable that is most important for the future number of people. The rate at which fertility falls determines whether the world population will peak at 8 billion people (as other studies contend) or at 12 billion people (as our results indicate). In order to have our population peak at 8 billion, we need to let fertility fall twice as fast as the (longer-term) empirical evidence suggests.

In other words, Fisher et al. argue that the data do not support the projections by IIASA and UN. Specifically, Fisher et al. contend that IIASA and UN place too much emphasis on trends in the recent decade; and ignore the evidence over a last half century and in cross-sections.

The First Order Draft of Chapter 3 reads:

IIASA (2001) and the UN (2004) are the only institutions that have produced updated projections for the world that extend to 2100. […] [T]he most recent central projections for global population are 1.4 to 2.0 billion (13 to 19 per cent) lower than the medium population scenario of 10.4 billion used in the SRES B2 scenarios.

A referee (me) pointed the authors to the Fisher et al. paper, and the authors responded.

Noted, reference will be added (page 25, line 38), text will be moidified deleting the word “only”.

The Second Order Draft of Chapter 3 reads:

IIASA (2001) and the UN (2004) are the only major demographic institutions that have produced updated projections for the world that extend to 2100. […] [T]he most recent central projections for global population are 1.4 to 2.0 billion (13 to 19 per cent) lower than the medium population scenario of 10.4 billion used in the SRES B2 scenarios.

This sentence is essentially the same. However, a few paragraphs later, we read:

A small number of new population projections judged to be consistent with SRES storylines have been developed (Gruebler et al., in press; Fisher et al., in press; Hilderink, 2004).

A referee (me) protested against the interpretation that Fisher et al. “are consistent with SRES”. The authors replied

Need to check with Brian O’Neil

The result is the wording in the final chapter as reproduced above. There are three papers cited in evidence. One is peer-reviewed, two are not. The peer-reviewed paper is misrepresented – despite protests in two rounds of review – and the chapter supports the conclusion of the gray literature, without alerting the reader that these is a wider range of opinion.

In the Summary for Policy Makers, we read

Studies since SRES used lower values for some drivers for emissions, notably population projections.